Stretching a RadGrid to 100% of the browser height can show as "squashed" when the grid is AJAX-enabled. Even without AJAX involved, stretching RadGrid requires setting the grid Height to "100%" and the Height style of all parent controls to "100%". Setting RadGrid Height alone outputs this disappointing view where the data is squashed to a single text line.
You'll see this same "compact" view of the data in IE, FireFox ,Chrome and Safari. Add the style below to set HTML, Body and Form tags height to 100% and hide margin, padding and scrollbars.